Consolidation of oil-bearing formations



Dec. 16, 1969 E. H. BRUlsT 3,483,926

CONSOLIDATION OF OIL-BEARING FORMATIONS Filed July 25, 1968 SEPARATOR CONTROL UNIT INVENTOR:

EDMONO H. RuesT BWM.

United States Patent O US. Ci. 166-'288 9 Claims ABSTRACT OF THE DISCLGSURE A process for consolidating an unconsolidated earth formation that is encountered by the borehole of a well by casing the borehole to a depth at least below the formation to be consolidated. A unit containing both perforating means and heating means is then suspended within the well and liquid is removed from the well at least to a depth adjacent the formation to be consolidated. Gas is pumped into the well until the pressure of the gas within the well is at least substantially equal to the formation fluid pressure at the depth of the formation to be consolidated. The casing is perforated and heated While pressure on the gas is maintained at least substantially equal to the formation pressure. Finally, the temperature of any thermally solidiable materials within the pores of the formation to 'be consolidated is increased to the point at which they solidify within the pores of the formation.

BACKGROUND OF THE INVENTION Field of the invention This invention generally relates to the production of oil petroleum or minerals from loosely consolidated or uncemented formations. More particularly, the invention concerns a process of consolidating an unconsolidated earth formation encountered by the borehole of a Well and extracting organic materials therefrom.

Description of the prior art ln production of petroleum from subterranean reservoirs, many wells are drilled into or through loosely cemented or unconsolidated formations. When such a well is placed on production, sand is often carried from the formation by the fluid and deposited in the well bore. Some sand is usually entrained in the produced fluid thus causing severe erosion and damage to equipment which is employed in the production of the fluid. The production of the sand interferes -with the normal production operations and gives rise to numerous operating problems. It can generally be said that in the production of a fluid from a loosely consolidated formation, workovers are frequently necessary to remove sand from the bottom of the borehole. lf the erosion of the sand around the casing in the bottom of a borehole is sufficiently great, it will leave the casing inadequately supported and the casing may eventually buckle or collapse. In some instances, the sand problem is so severe that the well has to 'be abandoned. The magnitude of the problem, then, is seen to be considerable.

Various methods have been attempted or suggested to date for solving the problem of sand production in wells that penetrate consolidated formations. Two commonly used praAcuti/cksnare (l) gravel packing, and (2) plastic consolidgio n the gravel packing procedure, gravel is packed or otherwise placed so that all the oil produced must pass through the gravel pack before entering the production tubing. A common method is to pack the annulus between a slotted liner and the borehole wall. The gravel in effect acts as a filter permitting the oil to pass through but retaining the sand. The use of gravel 3,483,926 Patented Dec. 16, 1969 ICC packing to control the production of sand has proved in many cases to be quite helpful; however, gravel packing has many serious disadvantages. For example, future workovers in Wells having gravel packs are quite expensive. Furthermore, if a Water shut-off operation is desired in an oil-producing well, it is often necessary rst to remove the gravel pack and its associated equipment before the workover can commence. After the Workover has been completed, it is necessary to again gravel pack before testing the success of the workover operations. These all. add to considerable time and effort and, in many cases, wells are abandoned due to the cost of such operations.

Plastics such as phenol-formaldehyde have been used to consolidate the sand particles of the unconsolidated formations. Unfortunately, this system has a serious drawback in that the plastic injected into the formation is not evenly distributed; that is, the distribution is affected by the permeability Variations throughout the section. In other Words, most of the plastic goes into the more permeable zones with very little or none of the plastic going into the less permeable zones.

It has been proposed to consolidate an unconsolidated formation by heating the fluid in an isolated part of a well bore sulciently so that heat will be transferred into the formation thereby raising the temperature of the portion of the formation immediately surrounding the well bore as, for example, disclosed in a patent, No. 3,104,704, to Ortlofl et al. In such thermal sand consolidation processes, it is essential that gas be injected during the heating operation. In addition to supplying a reactant to facilitate the solidication of certain solidifiable materials, such as oil or other organic components, the injection of gas provides a means of conveying heat into the formation and ensuring that the permeability of the formation is retained when the formation becomes consolidated. When gas is flowing through the pores of a formation, it displaces any liquid that impedes its flow. When solidifiable liquids are solidified within pores of a formation through which gas is flowing, the solids form along the grain boundaries in locations in which they do not materially reduce the permeability of the formation.

In order to prevent formation fluid and sand from an unconsolidated formation from flowing into a cased well, it is essential that the pressure within the well approximately equals or exceeds the pressure within the formation when the casing is perforated. It is not practical to attempt to heat a formation to the temperature needed for thermal consolidation while the heater is immersed in a flowing or unconfined column of liquid because the maximum temperature which can be reached will be equal to the boiling temperature of those liquids at the prevailing pressure. These temperatures are generally too low to achieve thermal consolidation.

In certain prior art processes, expensive equipment is required in order to first pressurize and perforate a well, retrieve the cable and perforator, and then insert a heater. In the latter operation, it is necessary to insert the heater through a high-pressure wellhead lubricator. In most instances, the weight of the heater would be insufficient for the heater and its relatively large diameter electric cable to be lowered against the wellhead pressure. In a gas-filled well, the wellhead pressure is nearly as high as the formation pressure. The use of expensive equipment is required to force the heater and cable down through the sealing elements of the lubricator and this involves significant cost, time and wear of the long expensive heater cable.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved process for thermally consolidating an unconsolidated earth formation encountered by a well.

It is a further object of this invention to provide a thermal consolidation process wherein a selected amount of liquid and one or more selected gaseous reactants may be injected into an earth formation prior to or during the heating of the formation.

It is a still further object of this invention to provide a process for solvent extracting thermally consolidated organic materials contained within an earth formation before the permeability is reduced by the cooling of partially solidified materials.

The process of this invention is carried out by casing the borehole of a well at least below an unconsolidated formation encountered by the borehole. Liquid is removed from the well at least to a depth adjacent the formation to be consolidated, and a unit containing both heating means and perforating means is suspended within the WeILGas is pumped into the well until the pressure of the gas within the well is at least substantially equal to the formation uid pressure at the depth of the formation to be consolidated. The casing is` perforated and heated via the unit while pressure on the gas is maintained at least substantially equal to the formation pressure. Finally, the temperature of any thermally solidiable materials within the pores of the formation to be consolidated is increased to the point at which they solidify Within the pores of the formation.

Where an oxygen-free gas or gas with low oxygen content such as about 3% is used to pressurize the well7 the treated formation may be flushed before its permeability is reduced by the cooling of partially solidied materials. If such materials are allowed to cool during an inflow of formation fluids, they are apt to form viscous plugs reducing the receptivity to solvents that may be later injected.

In an added feature of the invention, it may be desirable to inject a selected relatively small amount of a readily soliditiable liquid, such as an aqueous solution or suspension of sugar or starch, or a readily cokable oil, prior to heating the formation.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a partly diagrammatic vertical sectional view showing the unit of the invention in position in a well bore opposite the formation to be treated; and

FIGURE 2 is a partly diagrammatic vertical sectional view showing the recovery of formation fluids from the well of FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGURE 1 of the drawing, there is illustrated a vertical cross-section or profile of a portion of the earth showing an unconsolidated oil bearing formation 11 which lies vertically intermediate an upper impervious formation 12 and a lower impervious formation 13. A well 14 is shown as extending from the earths surface 15 to the unconsolidated formation 11. Well 14 includes a casing 16 as is well known in the art. A unit 17, including a perforating device 18 coupled to the lowermost end of a heating device 19, is suspended within well 14 by means of a cable 20. Cable 20 is of suflcient strength to raise and lower unit 17 within well 14 and includes the necessary electrical conduits for conveying power from a surface control unit 21 to unit 17. Unit 1'7 is suspended within a tubing string 22 mounted in well 14 and cable 20 passes over suitable means for raising and lowering unit 17 within well 14, such as a pair of sheaves 23 and 24 controlled by unit 21. Sheave 24 may comprise a cable measuring sheave and sheave 23 may be coupled to a pulling unit mast 25 as is well known in the art.

Unit 17 is shown in FIGURE 1 positioned within well 14 at a point below a plurality of perforations 26. However, in operation, prior to perforating well 16, the tubing 22 is lowered adjacent the interval which is to be perforated and gas is pumped into die annular space between the casing 16 and the tubing 22 through inlet 16a displacing liquids from tubing 22 through outlet 22a. After all liquids have been removed to near the interval to be perforated, gas pressure is released and the tubing 22 is raised to the position as indicated in FIGURE i. Unit 17 is now lowered Within well 14 through a conventional wireline or cable type blow-out preventer 28 and into tubing string 22 by means of control unit 21 until the perforating device 18 of unit 17 is positioned adjacent the portion of the unconsolidated formation 11 desired to be consolidated. The blow-out preventer 2S is now packed off around the cable and gas is pumped into the well 14 through inlet 16a or outlet 22a until the pressure of the gas within well 16 is at least substantially equal to the formation iluid pressure at the depth of formation 11 desired to be consolidated.

Perforating device 18 is then actuated, through suitable electrical means in control unit 21 and cable 20, to perforate the casing 16 and through a sheath of cement 27 preferably surrounding casing 16 adjacent the formation 11 to be consolidated. With the blowout preventer 28 remaining packed off around the cable 20, unit 17 is lowered until the center of the hot zone of heating device 19 is adjacent the perforated section of well 16 and the interior of casing 16 is heated at a point near perforations 26 while pressure is maintained on the gas within well 16. Well 16 may also include an outer upper casing 29, if desired, as is well known in the art. Although only a pair of perforations 26 are shown in FIGURE 1, a plurality of perforations 26, in the sarne vertical plane or spaced horizontally, may be provided depending on the size of formation 11 and the area desired to be consolidated. The heating device 19 is actuated for a period of time sufcient to increase the temperature ot' thermally soliditiable materials within the pores of the formation to be consolidated to a temperature at which they solidify within the pores of the formation.

A stream of gas, such as air, nitrogen, oxygen, any desirable mixture of nitrogen and oxygen or a hydrocarbon gas may be injected into formation 11 through tubing string 22 or casing 16 while heating formation 11 so as to convey heat into formation 11 and ensure the permeability thereof when the unconsolidated sand becomes consolidated.

If desired, a source of free radicals may be carried along with the gas stream adapted to facilitate the solidication of any thermally solidificable materials within the unconsolidated earth formation 11 while heating formation 11 in the manner described in a patent, No. 3,250,- 329, to Prats. As disclosed therein, such a source of free radicals may include free-radical reactive gases such as oxygen, nitrogen dioxide, nitric acid, hydrogen peroxide, ozone or mixtures of these materials or other like materials of this class. The injection is carried out while heating the formation 11 and results in polymerization of the hydrocarbons within formation 11.

In like manner, a selected relatively small amount of a fluid having a carbohydrate entrained therein for enhancing the thermal consolidation of formation 11 may be injected into the formation 11 prior to heating formation 11 in the manner disclosed in a patent, No. 3,259,188, to OBrien. The subsequent heating of the formation 11 in the absence of oxygen results in carbonizing of the carbohydrates while the differential pressures between the borehole and the formation 11 are balanced. This step may be carried out simultaneously with the aforementioned free radical step, but the ox gen content should be low to prevent ignition, i.e., normally less than 3% O2.

Alternatively to pumping a gas into the formation 11 as l suggested hereinabove for carrying heat therein, an oxygen-free gas may be pumped into formation 11. Furthermore, -sufcient organic solvent may be pumped into the well 14 and forced into the pores of formation 11 by gas displacement so as to permeate the pores'containing solidied organic materials and solvent soluble organic material. Subsequently, the solvent soluble organic materials may be extracted from the pores by reducing the gas pressure within the well below that of the formation uid pressure and backflowing the solvent solution into well 14 and up tubing string 22 as will be discussed further hereinbelow and is well known in the art.

The foregoing steps of injecting a stream of gas to carry the heat into formation 11, introducing a source of free radicals therein and injecting a iiuid having carbohydrate contained therein may be carried out with respect to the oxygen-free gas procedure discussed hereinabove.

With the process of the invention disclosed hereinabove, the unit that includes the heating and perforating means can readily be lowered or raised a short distance, if it is desirable to reposition the heating means relative to the perforations, through the pressure seal at the Wellhead. Having both the heating and perforating means in the well at the time the pressurizing gas is injected avoids both costly delays and expensive equipment that would be required to first pressurize and perforate the well, then retrieve the cable and perforator, and then insert the heater. In the latter operation, it is necessary, as discussed above, to insert the heater through a high pressure Wellhead lubricator.

In operation, heat from heating means 19 flows outwardly through perforations 26 into formation 11, assisted by the injection of gas, if desired. The heat tends to heat the portion of formation 11 immediately surrounding casing 16 and causes the unconsolidated formation immediately surrounding the wellbore to be heated suiiiciently to cause a coke-like deposit to form, thus bonding the particles of sand together into a permeable consolidated zone or mass as illustrated at 30. To accomplish this, it has been found that heating means 19 should be raised to a temperature generally from about 400 F, to about 700 F. in the presence of oxygen. lf an oxygen-free gas is injected, temperatures generally from about 800 F. to 1600 F. are required.

The temperature of the heating means 19 should be maintained long enough for the section immediately surrounding the wellbore to reach a temperature approaching Athat of the heating means 19. The thickness of the consolidated shell need not be great; indeed it has been found that a consolidated shell from as thin as one to two inches is suiicient to support most formations adequately. The time required to reach the desired temperature immediately surrounding the wellbore depends largely upon the capacity of the heating means, the diameter of the borehole and the type completion. For example, if cement is behind the casing, a greater period of time will be required than if cement is not present. The required time can be determined through calculations or experiments. The minimum temperature at which consolidation of this process occurs will vary depending on such factors as type of oil in the reservoir and the reservoir pressure; also, the use of the various steps discussed hereinabove may shorten the consolidation time thus making the operation even more practical and inexpensive. These procedures also tend to increase the thickness and strength of the consolidated zone 30.

After the zone 30 has been consolidated, well 14 is ready to be placed on production. To accomplish this, unit 17 is removed from tubing string 22, tubing string 22 is packed at 31 if so desired and sand-free production is then produced through consolidated zone 30, perforations 26, and upwardly through tubing string 22 to a conventional separator 32 located at the surface 15 of the earth as is well known in the art and illustrated by the arrows in FIGURE 2.

Surface equipment for pulling tubing string 22 and generating the electricity for unit 17 have not been shown as suitable means are well known in the art. yIn carrying out the invention disclosed hereiabove, if suiiicient residual hydrocarbons are not present in the formation, such as in gas formations for example, residual hydrocarbons may be added.

I claim as my invention:

1. The process of consolidating an unconsolidated earth formation that is encountered by the borehole of a well, the process comprising the steps of casing the borehole to a depth at least below the formation to be consolidated;

removing liquid from the well at least to a depth adjacent the formation to be consolidated;

pumping gas into the well until the pressure of the gas within the well is at least substantially equal to the formation liuid pressure at the depth of the formation to be consolidated; suspending a unit containing both heating means for heating a formation and perforating means for perforating a casing within the well to a depth adjacent the formation to be consolidated;

perforating the casing via said unit adjacent the formation to be consolidated;

heating the interior of the casing via said unit at a point near a perforation While maintaining said pressure on the gas within the well at least substantially equal to the formation pressure; increasing the temperature of any thermally solidiable materials within the pores of the formation to be consolidated via said unit to a temperature at which they solidify within the ports of the formation; and

the steps of perforating the casing, heating the interior of the casing and increasing the temperatures of materials within the formation via said unit being carried out without removing said unit from the well between said steps.

2. The process of claim 1 including the step of injecting a stream of gas into the unconsolidated formation while increasing the temperature of any thermally solidifiable materials Within the pores of the formation so as to convey heat into the formation and ensure the permeability thereof when said unconsolidated formation becomes consolidated.

3. The process of claim 2 including the steps of introducing, while heating said formation and via said gas stream, a source of free radicals adapted to facilitate the solidification of any thermally solidiable materials Within the unconsolidated earth formation by polymerization of the hydrocarbons within said formation.

4. The process of claim 1 including the step of injecting, into said formation prior to heating said formation, a selected relatively small amount of a fluid having a carbohydrate entrained therein for enhancing the thermal consolidation of said formation.

5. The process of claim 1 including the step of reducing the pressure of the gas within the well at least below the formation pressure; and backflowing formation iiuids from the formation and into the well.

6. The process of consolidating an unconsolidated earth formation that is encountered by the borehole of a well, the process comprising the steps of casing the borehole to a depth at least below the formation to be consolidated;

removing liquid from the well at least to a depth adjacent the formation to be consolidated; pumping an oxygen-free gas into the well until the pressure of the gas within the well is at least substantially equal to the formation fluid pressure at the depth of the formation to be consolidated;

perforating the casing adjacent the formation to be consolidated;

heating the interior of the casing at a point near a perforation while maintaining said pressure on the gas within the well at least substantially equal to the formation pressure; increasing the temperature of any thermally solidiiiable materials within the pores of the formation to be consolidated to a temperature at which they solidify Within the pores of the formation;

pumping suicient organic solvent into the well and forcing said solvent into said pores by gas displacement so as to permeate the pores of the formation which contain solidified organic materials therein; and

extracting solventsoluble organic materials from said pores by reducing the gas pressure within the well below that of said formation uid pressure and backiiowing solvent solution into the well.

7. The process of claim 6 including the step of injecting a stream of gas into the unconsolidated formation While heating said formation so as to convey heat into the formation and ensure the permeability thereof when said unconsolidated formation becomes consolidated.

8. The process of claim 7 including the step of introducing, While heating said formation and via said gas stream, a source of free radicals adapted to facilitate the solidication of any thermally solidiiiable materials within the unconsolidated earth formation by polymerization of the hydrocarbons Within said formation.

9. The process of claim 6 including the step of injecting, into said formation, prior to heating said formation. a selectedV relatively small amount of'a fluid having a carbohydrate entrained therein for enhancing the thermal consolidation of said formation.

References Cited UNITED STATES PATENTS 3,104,705 9/1963 Ortloif etal. 166-288 3,121,462 2/1964 AMartin et al. 166-288 3,195,631 7/1965 Smith 166-297 3,250,329 5/1966 Prats 166--288 3,259,188 7/1966 OBrien 166-288 X 3,292,701 12/1966 Goodwin et al. 166-288 X 7 CHARLES E. OCONNELL, Primary Examine-r I. A. CALVERT, Assistant Examiner U.S. C1. X.R 166-55.1, 297, 305 

